1. Field of the Invention
The present invention relates to a flame retardant for polyolefins. More particularly, the present invention relates to a halogen-free flame retardant for polyolefins.
2. Description of the Related Art
Polyolefins are light and have high strength, and have excellent water resistance, chemical resistance and electrically insulating properties and can be easily molded and processed. Accordingly, polyolefins are widely used as materials of electric appliances, automobile parts and construction materials.
However, polyolefins are defective in that they are easily combustible. Therefore, various processes for rendering polyolefins flame-retardant have been proposed. Among these processes, there is most popularly adopted a process in which an organic bromine compound or organic chlorine compound and antimony trioxide are added to a polyolefin. As the organic bromine or chlorine compound, there can be mentioned, for example, decabromodiphenyl oxide, a bisdibromopropyl ether of tetrabromobisphenolsulfone, a bisdibromopropyl ether of tetrabromobisphenol A, tris-2, 3-dibromopropyl isocyanurate and a Diels-Alder reaction product of hexachlorocyclopentadiene. Furthermore, there have been proposed various other processes, for example, a process in which a metal hydroxide is added as disclosed in Japanese Unexamined Patent Publication Nos. 50-34643, 50-133247 and 51-128194, a process in which a metal hydroxide and ammonium polyphosphate are used in combination as disclosed in Japanese Unexamined Patent Publication No. 54-22450, a process in which melamine is added as disclosed in Japanese Unexamined Patent Publication Nos. 54-15952 and 56-103233, a process in which ammonium polyphosphate and a melamine-formalin resin are used in combination as disclosed in Japanese Unexamined Patent Publication No. 55-129435, and a process in which an inorganic compound is added.
When a halogen compound is used, since a hydrogen halide is formed by thermal decomposition, a mold or the like is easily corroded at the molding step. Furthermore, when a fire takes place, evacuation is inhibited by an irritating smell, and at the time of incineration, a stimulative smell is generated or an incinerator is corroded. When an inorganic compound such as ammonium polyphosphate or a metal hydroxide is used, since the flame-retardant effect is low, it is necessary to add such an inorganic compound in a large quantity. If the inorganic flame retardant is incorporated in a large quantity, the specific gravity of the polyolefin is increased and the strength, especially the impact resistance, is degraded.